Modern television distribution systems can use a mixture of either analog or digital modulation formats in the same frequency range (allocation). For example, for United States terrestrial television distribution systems, the frequency assignments and channel spacing are pre-defined and regulated by the Federal Communication Commission (FCC), but the modulation mode for such signals can be either NTSC (National Television System Committee, as described in Recommendation ITU-R BT.470-6) or 8-VSB (8-level Vestigial Sideband) provided by the ATSC (Advance Television System Committee) Standard “ATSC Standard: Digital Television Standard (A/53), Revision D, Including Amendment No. 1,” July, 2005. For cable television distribution systems, the frequency assignment and channel spacing (frequency gap between channels) can vary from cable system to cable system as the system is closed and thus amenable to less regulation. In addition to the NTSC and 8-VSB modulation mode transmissions, digital QAM (Quadrature Amplitude Modulation) modulation modes (256 QAM, 64 QAM) may be used as provided by SCTE (Society of Cable Telecommunications Engineers) Standard ANSI/SCTE 07 2000 “Digital Video Transmission Standard for Cable Television.” Furthermore, side information about the cable system can also be present in the cable signal, as is provided by FDC channels (Forward Data Channel), as described by SCTE Standards “ANSI/SCTE 55-1 Digital Broadband Delivery System: Out of Band Transport Part 1: Mode A,” and “ANSI/SCTE 55-2 Digital Broadband Delivery System: Out of Band Transport Part 1: Mode B.”
Channel scan operations can be performed to find television signals that are available in the frequency range and to determine the modulation formats and frequencies of the signals from a source (e.g., a local cable operator) of the signals. Identification of terrestrial and cable channels available for reception is an important feature used in television and set-top receivers. The existence of digital television modulation formats in addition to analog-only modulated signals significantly increases the time to identify the frequency of operation (for a cable system) and the modulation mode(s) of the transmissions. Without prior knowledge of the modulation formats and frequencies of the available signals, identification of the transmitted modulated signals is a difficult and time consuming process, typically involving fully acquiring an incoming signal and evaluating its data and/or video and/or audio content.